1. Field of the Invention
The present invention relates to an apparatus and method for reclaiming contaminated scrap metal, more particularly to an improved reverberatory furnace for melting scrap and collecting the combustible portion of the contaminates contained thereon. The furnace then quantifies the combustible contaminates and uses them as additional fuel for heating the furnace and the metal contained therein, which reduces fuel usage and eliminates the release of most pollution from the furnace.
2. Description of the Prior Art
Used metals are a major material resource used in making new products. In the aluminum industry, re-melting of aluminum scrap consumes only five percent of the energy required to make primary aluminum from bauxite. A common source of aluminum scrap includes turnings and borings from machine shops, the waste aluminum cut from the edges of aluminum sheets after rolling, the material remaining after punching or stamping, or scrapped aluminum products. This scrap material is collected and baled into various size bales, then shipped to recycling plants having furnaces particularly designed to process scrap metal. The metal is recycled by melting in a furnace and combining the melted scrap metal with molten metals of a predetermined purity to obtain the appropriate alloy. A major problem with scrap metal is that it contains various amounts of contaminants, particularly oils, grease, other lubricants, paints, lacquers etc., which are normally burnable hydrocarbons and will be volatilized during the melting process. Without appropriate cleaning of the exhaust fumes, at high-cost, these pollutants will be expelled into the atmosphere. A number of improvements to scrap metal furnaces have been made in an effort to eliminate the contaminants by separately burning the exhaust gases or by re-circulating the gases through the main burners.
For example U.S. Pat. No. 3,933,343 issued to Robert K. Rawlings discloses a well-type melting furnace that is divided into two communicating wells: a receiving well for the scrap material and a main holding well for holding the molten metal. A fume collection hood over the scrap receiving well collects the combustible fumes that issue from the scrap as it is melted and conducts the fumes through ductwork to a burner in the main holding well. The burner is operated at a high air level to ensure complete burning of the combustible fumes when they are received and a large amount of air is drawn into the scrap receiving well by the blower fan that transfers the fumes from the scrap receiving well to the burners in the main holding well. The blower fan maintains the scrap receiving well at a negative pressure, permitting air to enter from the outside. A sensor in the exhaust stack determines whether all exhaust fumes have been burned, and if they have not, additional air is added to improve combustion. The sensor in the exhaust stack provides a delayed indication of incomplete burning so that the adjustments are always accomplished after incomplete burning has commenced and contaminants have been exhausted through the stack. In addition, as long as burning is complete the sensors do not indicate any adjustment for reduction of the oxygen supply to the main hearth. If the temperature drops, fuel is furnished to the burners to raise the temperature. If the level of oxygen is considered too high, an adjustment is made by closing a valve, however, there isn't any indication of the basis for determining that the level is too high or the basis for the amount of adjustment that should be made.
U.S. Pat. No. 4,319,921 issued to Pryor, et al. discloses a scrap metal furnace that also transfers the vaporized combustibles to the main hearth through the main hearth burners. The duct work transferring the vapors includes a burner that is aimed downstream toward the main hearth. The burner pulls the gases from the scrap charging chamber, burns a portion of the combustible gases, and passes the remainder through one of the main hearth burners.
Notwithstanding the existence of such prior art furnaces, it remains clear that there is a need for a furnace that will adjust the amount of fuel provided to the burners based upon the amount of hydrocarbons that are being added to the main hearth. This will ensure complete burning is accomplished without fuel wastage or excess oxygen. NO.sub.x is a pollutant that is created when nitrogen and free oxygen are available in a high temperature environment, there is a need for a furnace that produces low levels of NO.sub.x.